As a reciprocating engine of this type, a reciprocating engine has been proposed in JP-A-5-180069 in which, in order to reduce sliding frictional resistance between a side surface of a piston and an inner surface of a cylinder which increases as a connecting rod is inclined in an explosion stroke (combustion stroke), a second piston ring (second ring) adjacent to a first piston ring (top ring) is inclined with respect to the first piston ring, and a combustion chamber and an annular gas chamber between the first and second piston rings are communicated through a gas passage. In such a reciprocating engine, the support of the piston (gas-pressure support) on the thrust side occurring on the basis of the gas pressure of the annular gas chamber is increased by tilting the second piston ring, so as to reduce the sliding frictional resistance between the inner surface of the cylinder, on the one hand, and the side surfaces of the piston rings and the side surface of the piston, on the other hand, due to the lateral pressure of the piston.
In addition, as another reciprocating engine of this type, a reciprocating engine has been proposed in JP-A-5-5459 in which, in order to reduce the sliding frictional resistance between the inner surface of the cylinder and the side surface of the piston in the reciprocating motion of the piston, a second piston ring (second ring) adjacent to a first piston ring (top ring) is inclined with respect to the first piston ring. In such a reciprocating engine, the lateral pressure on the thrust side occurring on the basis of combustion gases is increased by tilting the second piston ring, so as to reduce the thrust-side sliding frictional resistance between the inner surface of the cylinder, on the one hand, and the side surfaces of the piston rings and the side surface of the piston, on the other hand, which can increase on the basis of the gas pressure and the like of the combustion gases in the combustion chamber with respect to the piston.
Incidentally, in such a reciprocating engine, if the second piston ring is inclined to gas-pressure support the piston by generating gas pressure which resists the lateral pressure of the piston, the volume on the thrust side of the annular gas chamber defined by the first and second piston rings becomes greater than the volume on the counter-thrust side thereof. Therefore, a required amount of combustion gases in the combustion chamber cannot be speedily introduced into the annular gas chamber through a single gas passage. Hence, it is difficult to substantially reduce the sliding frictional resistance between the cylinder, on the one hand, and the piston rings and the side surface of the piston, on the other hand, by generating desired supporting force. In a case where the second piston ring is inclined greatly or in a case where the period of communication between the combustion chamber and the annular gas chamber per reciprocating motion becomes short due to the high-speed rotation of the reciprocating engine, it can become even more difficult to introduce a required amount of combustion gases in the combustion chamber speedily into the annular gas chamber.
In addition, with the above-described other reciprocating engine, if the second piston ring is inclined greatly so as to generate large lateral pressure on the thrust side, there is a possibility that the inclined second piston ring interferes with an oil ring. Accordingly, it is difficult to substantially reduce the sliding frictional resistance between the cylinder, on the one hand, and the piston rings and the side surface of the piston by generating desired lateral pressure.
The present invention has been devised in view of the above-described aspects, and its object is to provide a reciprocating engine which is capable of speedily introducing a necessary amount of gases in the combustion chamber into and causing it to act in the annular gas chamber with necessary force during a starting period of the fall of the piston in the explosion stroke and of generating a desired gas-pressure supporting force, thereby making it possible to substantially reduce the sliding frictional resistance between the cylinder, on the one hand, and the piston rings and the side surface of the piston, on the other hand.
Another object of the present invention is to provide a reciprocating engine which is capable of eliminating the interference of the piston ring with the oil ring and of generating the desire lateral pressure, thereby making it possible to substantially reduce the sliding frictional resistance between the cylinder, on the one hand, and the piston rings and the side surface of the piston, on the other hand.